The conventional Staggered Steel Truss System (SSTS) originated as a design project at MIT in the 1960s. SSTS is a framing system in which the floor girders are full story depth trusses, and are buried in the walls. It gets its name from staggering the trusses at each floor level so that the floor planks are supported by the top chord of a truss at one end, but the bottom chord of an adjacent truss at the other end, as best shown in FIG. 11. For more explanation of an SSTS, please see the paper entitled “Staggered Truss Framing System in Areas of Moderate-High Seismic Hazard,” by Kevin S. Moore, in the 2005 NASCC Proceedings, San Antonio, Tex., February 8-11. The disclosure of this paper is hereby incorporated by reference in its entirety.
SSTS was originally thought to be a good seismic performer, and as a result, a number of these types of building were built. Further analysis later showed that they present a seismic hazard. In ordinary buildings, the vertical and lateral bracing are different systems. In SSTS, however, the truss members are both bracing members and vertical support members. The normal yielding and buckling of braces used to dissipate seismic energy could cause vertical collapse. Notification when out to the design community in 2005. Since that time, no staggered steel truss buildings have been built in high seismic areas.
Recently, much research has been done in trying to create a SSTS building that would provide good seismic performance. So far all of the attempts have focused on the center panels of the trusses based on know designs of a system called the Special Ductile Truss System (SDTS), which is know to be very seismically robust. A SDTS concentrates all of the yielding and buckling of the system in the center panel. One difference between SSTS and the SDTS is that SSTS employs full floor-to-floor depth trusses and the SDTS does not. Please see the presentation entitled “Challenges of Using Steel Staggered Truss Framing Systems in High Seismic Regions: Behavior, Issues, and Possible Solutions” presented by Shih-Ho Chao, Assistant Professor of Civil Engineering, University of Texas, Arlington, at the Quake Summit, NEES and MCEER Annual Meeting, Buffalo, N.Y., Jun. 10, 2011. The disclosure of this presentation is hereby incorporated by reference in its entirety.